1. Field of the Invention
This invention relates to the field of converting synthesis gas to propylene. More particularly, it relates to a stepped process wherein unconverted synthesis gas and ethylene, produced via a Fischer-Tropsch reaction, are hydroformylated and then dehydrated to produce additional propylene.
2. Background of the Art
Much research has been devoted to processes using synthesis gas (“syngas”), a mixture of hydrogen gas and carbon monoxide gas, as a starting material. Such processes have been customized to produce a wide variety of desirable olefins, and particularly higher olefins, which are defined herein as those having three or more carbons (C3+). Many of these processes employ a Fischer-Tropsch (FT) reaction, which uses syngas obtained from coal, natural gas, or biomass as a substitute for petroleum starting materials, and employing a metal-based catalyst, such as one based on cobalt (Co), iron (Fe), or ruthenium (Ru). Where these processes are employed to produce olefins, they may be referred to as “Fischer-Tropsch-to-Olefins” (FTO) processes. Unfortunately, such processes tend to produce only small amounts of olefins, and in particular, small amounts of propylene, despite the fact that the propylene may be the dominant product. This may be undesirable where propylene is the production target, particularly for uses as a starting material to make, e.g., polypropylene, acetone, phenol, isopropanol, acrylonitrile, propylene oxide, and/or epichlorohydrin.
Means of enhancing production of propylene have included catalyst substitutions and modifications; modifications of pressure, temperature and feed gas; and alterations of stoichiometries. For example, U.S. Pat. No. 4,590,314 (Kinkade) discloses a selective reaction of a Cn olefin with carbon monoxide (CO) and hydrogen (H2) in the presence of a catalyst consisting essentially of molybdenum sulfide and an alkali metal or alkaline earth metal compound to form a Cn+1 alcohol. In the formula “n” is a positive integer equal to or greater than 2.
Despite the many substitutions, modifications, and alterations applied to the FTO process over the years, however, there remains in the art a need for processes that can produce propylene, in particular, in larger total amounts.